The aid agencies said in a dramatic statement from the capital Khartoum that the humanitarian workers in Darfur have been "holding the line for the survival and protection of millions" of people affected by the fighting in Darfur.
"That line cannot be held much longer," said the agencies, including the World Food program, United Nations High Commissioner for Refugees, United Nations Children's Fund, World Health Organization and U.N. Development Program.
The violence in Darfur has left more than 200,000 people dead and displaced 2.5 million since 2003, when ethnic African rebels began fighting the central Khartoum government, charging it with neglect.
The government has been accused of unleashing the Janjaweed paramilitary group of Arab nomads in response.
The U.N. groups also said the violence has included relief workers, 12 of whom have been killed in the past six months -- more than the previous two years combined, according to the Associated Press.
"It is completely unacceptable for our staff to have to risk their lives while helping the people of Darfur," said Paul Smith-Lomas, Oxfam's regional director, Reuters reported.
The roads in many portions of west and north Darfur are so unstable that staff can only travel via expensive helicopter flights.
Government-imposed restrictions on travel have hindered aid efforts as well, according to Reuters.
About 7,000 African Union peacekeepers are struggling to guarantee a cease-fire in Darfur signed by the government and one rebel group.
Khartoum opposes a U.N. resolution for over 20,000 U.N. troops to replace the AU forces.
